glaciers

“RIVERS OF ICE” Mass movement of frozen ice on land Form at high elevations or high altitude Last extension of ice here began 20,000 years ago and receded about 10,000 years ago. Today only covers 10% of land surface

Ice Flow Glaciers are not static they are dynamic Formation: A steady accumulation of snow piles up and compresses layers beneath – these compressed layers turn into ice Force of gravity continuously pulls ice downward Movement: Fastest ice is found on the surface at center of valley Rate varies from a few cm to meters per day.

There are 3 Categories of Glaciers 1. Valley (Alpine) Glaciers found in mountainous regions high altitudes Ex. Alps (New Zealand and Europe), Rockies Fanz Joseph Glacier – New Zealand

Valley or Alpine Glacier It occupies a valley in the mountains. The mountains are alpine, that is bare and jagged due to glaciation. Outlet glacier of Juneau icefield in Alaska. Dark stripes are medial moraines.

Ice Sheets (Continental Glaciers) Much larger Flow direction is from an area of thick ice to thin ice Ex. Greenland, Antarctica Ellesmere Island, Canada

3. Tidewater Glacier Flow far enough to reach out into the ocean Create icebergs Vertical calving base and small bergs floating in the sea Hubbard glacier, Alaska

Snow calving

Glacial Retreat Kilimanjaro, 1993 top, 2000 bottom – glacial retreat Alaska's Glacial Retreat Alaska's glaciers are receding at twice the rate previously thought, according to a study published in the July 19, 2002, issue of the journal Science. These two images show Portage Glacier, near Anchorage, Alaska, in about 1950 and in July 2001. The ice has pulled back nearly out of sight, leaving behind a glacial lake.

Glacial advance and retreat

Budget of a Glacier Glacier accummulation = snow adds to the weight of a glacier Glacier Wastage (ablation) = melting and calving. When accummulation is greater than wastage = glacier advances When accummulation is less than wastage = glacier retreats If accummulation = Wastage = glacier remains stationary Calving = breakage of ice forming icebergs

Glacial Erosion – Two Key Methods Plucking and Abrasion Features of Glacial Erosion: U-shaped valleys, sharp ridges (Aretes), pyramid peaks (Horns), water-filled valleys (Fjiords), and bowl shaped valleys (Cirques.

Glacial Erosion Sharp ridges and pyramid peaks Deep glacial carved fjord valleys

Striations and Grooves Indicate orientation but not direction

Depositional Features of Glaciers aka Glacial Dump Drift = any sediment deposited by moving ice 2 Types: Stratified Drift = well-sorted sediments deposited by streams (meltwater) Till = unsorted sediment, deposited by moving ice

Deposits of Till ｷ lateral moraines form along valley walls ｷ medial moraines form where 2 lateral moraines meet ｷ end moraine left at terminus of glacier where it retreats This photo shows two medial moraines (blue arrows) as seen from the air. The black arrows point to lateral moraines that have formed along the sides of the valley wall. Where the two main glaciers shown in the photo flow together, their lateral moraines join to form a medial moraine. The medial moraine on the right formed in the same way, however we can't see where the glaciers flow together to form the moraine.

Drumlins A drumlin is tear-shaped ridge showing direction of ice flow Low smoothly rounded elongated hill, of compact glacial till. Built under the margin of the ice and shaped by its flow., or carved out of an older moraine by readvancing ice. Its longer axis is parallel to the direction of the movement of ice. Blunt nose points in the direction from which the ice approached. Gentler slope tapering in the other direction. Height 8-60 m, average is 30 m, length 400 – 2000 m, average 1500m.

Drumlins Typical drumlin on a farm in Wisconsin, shows the direction of the glacier

Glacial Erratics Compositon of the deposit is different from the bedrock below Rock fragment carried by glacial ice, deposited at some distance from the outcrop from which it was derived. Generally resting on bedrock of different lithology (color, composition …) Glacial erratic near Calgary, Canada Central Park, besides being a world-class urban resource, is a showcase of New York City geology. The beautifully exposed outcrops of schist and gneiss bear traces of the ice ages, when continental glaciers scraped their way across the region leaving grooves and polish on the tough bedrock. When the glaciers melted, they dropped whatever they were carrying, including some large boulders like this. The rock has a different composition from the ground it sits on and clearly comes from elsewhere. Boulders like this are called erratics.

Deposits of Stratified Drift Kame :a small hill forms where sediments accumulate beneath ice. Esker: forms from under-glacial streams Kettle: a depression that can be water-filled Kames and kettles Kame is a mound, knob or short irregular ridge. Composed of stratified sand and gravel, deposited by subglacial stream as a fan or delta at the margin of a melting glacier, by a superglacial stream in a low place or hole on the surface of the glacier. Esker: serpentine ridge of roughly stratified gravel and sand deposited by a stream flowing in or beneath the ice. Kettle: depression in the glacial drift formed by the melting of a detached block of stagnant ice buried in the drift – common in kame fields

Kames

Eskers One of many eskers running across the northwest of Canada

Muir Glacier 1941 and 2004

Massive melting – Holgate glacier, Alaska 1909 and 2004